The present invention relates to a workpiece measuring machine and has particular reference to a machine adapted for scanning the surface of a workpiece to determine the shape thereof.
A variety of forms of measuring machine are currently in use each of which is more or less suited to carry out measurements on workpieces as diverse as small engineering piece parts, and large scale parts such as car bodies or aircraft wings. These have conveniently been classified into ten categories in a report commencing on page 11 of the ASME standard reference ASME B89.1.12M-1990, the categories including the well-known bridge machines, gantry machines, or cantilever machines. The machines may have either fixed or moving tables on which the workpiece is carried.
The philosophy behind the design of the machines has always been that the table used for supporting the workpiece has to be relatively massive, (traditionally a large granite slab) in order to avoid distortions occurring when heavy workpieces are mounted on the table. This has been particularly so in the moving bridge machines in which the tracks on which the bridge moves are formed on the table. Thus the table also has to be rigid enough to avoid distortions due to the movements of the bridge, which itself is a relatively massive structure in order to support the other moving parts of the machine.
In the fixed bridge and gantry types of machines, movements of the largest masses are avoided, but the fixed supports still are of relatively massive construction to avoid distortions. This leads to a lack of flexibility in the design, in that, in order for the designer to provide a range of machine sizes, a range of bridge and gantry structures have to be designed.
A similar problem is present for the designer of the cantilever machines, in which, a vertical support structure, or base, is required to provide a support at one side of the machine and on which the movable carriages are mounted. The height of the support determines the height of the working volume of the machine, so that to provide a range of working volumes, a range of machines is needed each with a different size of vertical support structure. Since the vertical support structure has to provide a rigid support for the moving carriages, once again the design philosophy has been to make it as a relatively massive rigid block.
Thus prior art machines have traditionally been heavy and. expensive, because of the relatively massive structures provided to give the required rigidity of construction.